Project Summary Acute lung injury and its more severe form, acute respiratory distress syndrome (ARDS), are devastating illnesses with high rates of incidence and high mortality rates. Patients with acute lung injury are typically provided supplemental oxygen using positive pressure mechanical ventilation, but this can lead to additional injury, termed ventilator- induced lung injury (VILI). The long term objective of this proposal is to improve understanding of the mechanisms by which overdistention (or stretch) of pulmonary epithelial cells contributes to ventilator-induced lung injury. The central hypothesis is that overdistention contributes both to the initiation of epithelial injury through loss of cell adhesion and to inhibition of repair mechanisms through decreased cell migration. Mechanisms of the initiation of VILI will be investigated using rats exposed to acid injury or surfactant depletion and direct visualization of airspace mechanics by microfocal X- ray imaging. A combination of in vitro, in vivo, and ex vivo approaches will be used to investigate the hypothesis that mechanical stretch causes loss of cell adhesion and inhibition of repair mechanisms through focal adhesion kinase (FAK) signaling. These approaches include primary cultures of rat alveolar type II (AT2) epithelial cells isolated from rats following mechanical ventilation, exposure of cells to mechanical stretch in vitro, and confocal microscopy of isolated rat lungs. Finally, atomic force microscopy will be used to test the hypothesis that localized changes in mechanical stiffness regulate the repair mechanisms of AT2 cells in culture. The proposed studies will investigate the mechanisms that contribute to lung injury during mechanical ventilation and provide new insights into mechanotransduction, the process of converting mechanical signals to biological signals.